This invention relates to mechanical delay lines and, more specifically to mechanical delay lines wherein a coaxial cable is moved axially with respect to a contact member to effect a change of the cable's effective electrical length.
The principal and purpose of such devices are well known in the art. By proper mechanical positioning of the cables, the effective electrical length of the co-axial conductors can be changed to provide a desired phase shift to establish a desired time-delay between the application of a signal to the input end of the conductors and the emergence of the signal from the output end.
Examples of related devices are illustrated and described in U.S. Pat. Nos. 2,379,047; 2,407,147; and 2,468,147. The first of these patents shows two concentric conductors 16, 17 whose effective length is varied by means of an axially movable contact in the form of a spring 2 carried by a carrier nut 8, which is mounted on a lead screw driven by a controllable motor. The spring 2 occupies the space between the two concentric conductors 16, 17, and short-circuits the two conductors at the position to which it is moved.
U.S. Pat. No. 2,468,147 discloses a co-axial line having an outer conductor 1 and an inner conductor 2. A slidable sleeve 3 is mounted for axial movement about the central conductor 2, and terminates in a piston-like head 4 inside the coaxial section. As the sleeve 3 is moved by a rack and pinion arrangement, the piston head 4 couples the inner and outer conductors at a changing position along the length of the conductors.
U.S. Pat. No. 2,407,147 shows a device in which a short-circuiting member 37 has fingers 22 contacting an outer cylindrical conductor 10, and fingers 21 contacting an inner cylindrical conductor 11.
In addition to the foregoing devices, presently available mechanical delay lines are known wherein semi-rigid coaxial cables are moved axially into and out of a coaxial cavity, to change the location at which their inner and outer coaxial conductors are contacted by respective, non-moving elements within the housing. The change in location of the contacting members along the cable changes the effective electrical length of the coaxial conductors. These devices are sold by such companies as Arra Inc. (Bay Shore, N.Y.), Sage Laboratories, Inc. (Natick, Mass.) and Precision Tube Company, Inc. (North Wales, Pa.). These mechanical "delay lines" are sometimes referred to as "phase shifters", and it is understood that the two terms are also used interchangeably herein.
The use of known mechanical delay lines has been limited by wear-related problems, as well as by difficulties in precisely setting the position of the movable coaxial cable to achieve the desired delay with absolute accuracy.. The wear-related problems have arisen most noticably from the sliding contact of the shorting elements against the coaxially-extending conductors. Consequently, mechanical delay lines have been used for relatively few applications, wherein the number and frequency of adjustments is minimal. Typically, such adjustments were made only once for a fixed phase adjustment. Adjustment methods have included screwdriver-type adjustments, micrometer adjustments, or the use of a slow moving motor.